This invention relates to lasers and amplifiers and in particular to fibre lasers and amplifiers and to colour centre lasers.
The active media of colour centre lasers are particular point defects in insulating crystals which introduce new allowed electronic transitions into the crystal's forbidden energy gap. This produces optical absorptions, and emissions, and therefore "colours" the normally transparent crystal.
In conventional colour centre lasers the active material is a cryogenically cooled single crystal slab. A stringent design of cryostat is required in order to maintain the crystal at the 77.degree. K. operating temperature (liquid nitrogen). The crystal slab is disposed on a cold finger of the cryostat within an optical cavity and provided with means for optically pumping the crystal slab for laser operation. There are various practical problems with such arrangements, particularly alignment difficulties since light has to be directed through windows of the cryostat.